Graded lower body negative pressure induces intraventricular negative pressures and incremental diastolic suction: a pressure volume study in a porcine model

Lower body negative pressure (LBNP) has been a tool to study compensatory mechanisms to central hypovolemia for decades. However, underlying hemodynamic mechanisms were mostly assessed non-invasively and remain unclear. We hypothesized that incremental LBNP reduces diastolic filling and thereby affects left ventricular (LV) diastolic suction (DS). Here, we investigated the impact of graded LBNP at 3 different levels of seal as well as during beta-adrenergic stimulation by invasive pressure-volume (PV) analysis. Eight Landrace pigs were instrumented closed-chest for PV assessment. LBNP was applied at three consecutive locations: I) cranial, 10cm below xiphoid process; II) medial, half-way between cranial and caudal; III) caudal, at the iliac spine. Level III) was repeated under dobutamine infusion. At each level, baseline measurements were followed by application of incremental LBNP of -15, -30 and -45 mmHg. LBNP induced varying degrees of preload-dependent hemodynamic changes, with cranial LBNP inducing more pronounced effects than caudal. According to the Frank-Starling mechanism, graded LBNP progressively reduced LV stroke volume (LV SV) following a decrease in LV end-diastolic volume. Negative intraventricular minimal pressures were observed during dobutamine-infusion as well as higher levels of LBNP. Of note, incremental LV negative pressures were accompanied by increasing DS volumes, derived by extrapolating the volume at zero transmural pressure, the so-called equilibrium volume (V0), related to LV SV. In conclusion, graded preload reduction shifts the PV loop to smaller volumes and end-systolic volume below V0, which induces negative LV pressures and increases LV suction. Accordingly, LBNP induced central hypovolemia is associated with increased DS.

The physiological effects of cardiac resynchronization therapy on aortic and pulmonary flow and dynamic and static components of systemic impedance

Background

Patients who improve following cardiac resynchronization therapy (CRT) have left ventricular (LV) remodeling and improved cardiac output (CO). Effects on the systemic circulation are unknown.

Objective

To explore the effects of CRT on aortic and pulmonary blood flow and systemic afterload.

Methods

At CRT implant patients underwent a noninvasive assessment of central hemodynamics, including wave intensity analysis (n = 28). This was repeated at 6 months after CRT. A subsample (n = 11) underwent an invasive electrophysiological and hemodynamic assessment immediately following CRT. CRT response was defined as reduction in LV end-systolic volume ≥15% at 6 months.

Results

In CRT responders (75% of those in the noninvasive arm), there was a significant increase in CO (from 3 ± 2 L/min to 4 ± 2 L/min, P = .002) and LV dP/dt_max (from 846 ± 162 mm Hg/s to 958 ± 194 mm Hg/s, P = .001), immediately after CRT in those in the invasive arm. They demonstrated a significant increase in aortic forward compression wave (FCW) both acutely and at follow-up. The relative change in LV dP/dt_max strongly correlated with changes in the aortic FCW (R _s 0.733, P = .025). CRT responders displayed a significant reduction in afterload, and a decrease in systemic vascular resistance and pulse wave velocity acutely; there was a significant decrease in acute pulmonary afterload measured by the pulmonary FCW and forward expansion wave.

Conclusion

Improved cardiac function following CRT is attributable to a combination of changes in the cardiac and cardiovascular system. The relative importance of these 2 mechanisms may then be important for optimizing CRT.

Predictors and prognosis of right ventricular function in pulmonary hypertension due to heart failure with reduced ejection fraction

Aims

Failure of right ventricular (RV) function worsens outcome in pulmonary hypertension (PH). The adaptation of RV contractility to afterload, the RV‐pulmonary artery (PA) coupling, is defined by the ratio of RV end‐systolic to PA elastances (Ees/Ea). Using pressure–volume loop (PV‐L) technique we aimed to identify an Ees/Ea cut‐off predictive for overall survival and to assess hemodynamic and morphologic conditions for adapted RV function in secondary PH due to heart failure with reduced ejection fraction (HFREF).

Methods and results

This post hoc analysis is based on 112 patients of the prospective Magdeburger Resynchronization Responder Trial. All patients underwent right and left heart echocardiography and a baseline PV‐L and RV catheter measurement. A subgroup of patients (n = 50) without a pre‐implanted cardiac device underwent magnetic resonance imaging at baseline. The analysis revealed that 0.68 is an optimal Ees/Ea cut‐off (area under the curve: 0.697, P < 0.001) predictive for overall survival (median follow up = 4.7 years, Ees/Ea ≥ 0.68 vs. <0.68, log‐rank 8.9, P = 0.003). In patients with PH (n = 76, 68%) multivariate Cox regression demonstrated the independent prognostic value of RV‐Ees/Ea in PH patients (hazard ratio 0.2, P < 0.038). Patients without PH (n = 36, 32%) and those with PH but RV‐Ees/Ea ≥ 0.68 showed comparable RV‐Ees/Ea ratios (0.88 vs. 0.9, P = 0.39), RV size/function, and survival. In contrast, secondary PH with RV‐PA coupling ratio Ees/Ea < 0.68 corresponded extremely close to cut‐off values that define RV dilatation/remodelling (RV end‐diastolic volume >160 mL, RV‐mass/volume‐ratio ≤0.37 g/mL) and dysfunction (right ventricular ejection fraction <38%, tricuspid annular plane systolic excursion <16 mm, fractional area change <42%, and stroke‐volume/end‐systolic volume ratio <0.59) and is associated with a dramatically increased short and medium‐term all‐cause mortality. Independent predictors of prognostically unfavourable RV‐PA coupling (Ees/Ea < 0.68) in secondary PH were a pre‐existent dilated RV [end‐diastolic volume >171 mL, odds ratio (OR) 0.96, P = 0.021], high pulsatile load (PA compliance <2.3 mL/mmHg, OR 8.6, P = 0.003), and advanced systolic left heart failure (left ventricular ejection fraction <30%, OR 1.23, P = 0.028).

Conclusions

The RV‐PA coupling ratio Ees/Ea predicts overall survival in PH due to HFREF and is mainly affected by pulsatile load, RV remodelling, and left ventricular dysfunction. Prognostically favourable coupling (RV‐Ees/Ea ≥ 0.68) in PH was associated with preserved RV size/function and mid‐term survival, comparable with HFREF without PH.

Physiological Impact of Afterload Reduction on Cardiac Mechanics and Coronary Hemodynamics Following Isosorbide Dinitrate Administration in Ischemic Heart Disease

Understanding the cardiac-coronary interaction is fundamental to developing treatment strategies for ischemic heart disease. We sought to examine the impact of afterload reduction following isosorbide dinitrate (ISDN) administration on LV properties and coronary hemodynamics to further our understanding of the cardiac-coronary interaction. Novel methodology enabled real-time simultaneous acquisition and analysis of coronary and LV hemodynamics in vivo using coronary pressure-flow wires (used to derive coronary wave energies) and LV pressure-volume loop assessment. ISDN administration resulted in afterload reduction, reduced myocardial demand, and increased mechanical efficiency (all P<0.01). Correlations were demonstrated between the forward compression wave (FCW) and arterial elastance (r=0.6) following ISDN. In the presence of minimal microvascular resistance, coronary blood flow velocity exhibited an inverse relationship with LV elastance. In summary this study demonstrated a reduction in myocardial demand with ISDN, an inverse relationship between coronary blood flow velocity and LV contraction-relaxation and a direct correlation between FCW and arterial elastance. The pressure volume-loop and corresponding parameters b The pressure volume loop before (solid line) and after (broken line) Isosorbide dintrate.

Effects of postural differences on intrapleural pressure during chest wall compression in healthy males

[Purpose] This study aimed to investigate the difference in intrapleural pressure between the supine and lateral decubitus positions during manual chest wall compression. [Participants and Methods] Eight healthy males participated in this study. The same physiotherapist performed chest wall compression on participants lying supine, and on their right and left sides. We noted changes in intrapleural pressure and lung volume in each participant during quiet breathing and chest wall compression. [Results] During chest wall compression, intrapleural pressure at the end-expiratory lung volume and the end-inspiratory lung volume were lower in the right and left decubitus positions than in the supine position. We observed the following low inflection points in the pressure-volume loops during chest wall compression: all participants in the supine position, no participants in the right decubitus position, and two participants in the left decubitus position. [Conclusion] Chest wall compression in the bilateral decubitus positions may not cause excessive intrapleural pressure on the airway and alveoli as compared to chest wall compression in the supine position.

Assessing Right Ventricular Function in the Perioperative Setting, Part II: What About Catheters?

An-depth assessment of right ventricular function is important in a many perioperative settings. After exploring 2-dimensional echo-based evaluation, other proposed monitoring modalities are discussed. Pressure-based methods of right ventricular appraisal is discussed. Flow-based assessment is reviewed. An overview of the state of current right ventricular 3-dimensional echocardiography and its potential to construct clinical pressure-volume loops in conjunction with pressure measurements is provided. An overview of right ventricular assessment modalities that do not rely on 2-dimensional echocardiography is discussed. Tailored selection of monitoring modalities can be of great benefit for the perioperative physician. Integrating modalities offers optimal estimations of right ventricular function.

Hemodynamics of Cardiogenic Shock

Cardiogenic shock (CS) represents an advanced state of morbidity along the pathophysiologic pathway of end-organ hypoperfusion caused by reduced cardiac output and blood pressure. Acute coronary syndromes remain the most common cause of CS. The spectrum of hypoperfusion states caused by low cardiac output ranges from pre-CS to refractory CS and can be characterized by an array of hemodynamic parameters. This review provides the foundation for a hemodynamic understanding of CS including the use of hemodynamic monitoring for diagnosis and treatment, the cardiac and vascular determinants of CS, and a hemodynamic approach to risk stratification and management of CS.

Calycosin-7-O-β-D-glucoside reduces myocardial injury in heat stroke rats

BACKGROUND/PURPOSE

Calycosin-7-O-β-D-glucoside (CG), a calycosin derivative compound derived from Astragali Radix, has protective effect against ischemia/reperfusion injury as well as bacterial endotoxin-induced vascular cell injury. In the present study, we ascertained whether CG could reduce myocardial injury in heatstroke rats.

METHODS

Heat stroke was induced by exposing anaesthetized rats to heat stress (43 °C for 70 min). Rats were given an i.p. dose of CG (26.8 mg/ml/kg) or vehicle solution (ml/kg) 15 min before the start of heat stress and immediately after termination of heat stress. Left ventricular performance, myocardial injury markers in the blood, and myocardial damage scores were assessed in heat stroke rats treated with or without CG. Additionally, cardiac levels of oxidative stress and inflammatory status were estimated simultaneously.

RESULTS

At the time point of heat stroke onset, compared with normothermic controls, group rats with vehicle solution had significantly decreased survival rate, increased hyperthermia, decreased left ventricular stress markers, and increased cardiac damage scores. Compared with group rats with vehicle solution, group rats with CG had significantly improved survival rate, decreased hyperthermia, decreased cardiac ischemic, inflammatory, and oxidative damage.

CONCLUSION

We thus conclude that myocardial injury can be a pressing need for the design of diagnostic and therapeutic modalities for heat stroke. In particular, our data indicate that CG protects against heat stroke in rats by mitigating myocardial injury.

Chronic overcirculation-induced pulmonary arterial hypertension in aorto-caval shunt

Pulmonary arterial hypertension is a common complication of congenital heart defects with left-to-right shunts. Current preclinical models do not reproduce clinical characteristics of shunt-related pulmonary hypertension. Aorto-caval shunt was firstly described as a model of right ventricle volume overload. The pathophysiology and the possible determination of pulmonary arterial hypertension of different periods of shunt exposure are still undefined. A method to create standardized, reproducible aorto-caval shunt was developed in growing rats (260±40 g). Three groups of animals were considered: shunt exposure for 10 weeks, shunt exposure for 20 weeks and control (sham laparotomy). Echocardiography and magnetic resonance revealed increased right ventricular end diastolic area in shunt at 10 weeks compared to control. Hemodynamic analysis demonstrated increased right ventricular afterload and increased effective pulmonary arterial elastance (Ea) in shunt at 20 weeks compared to control (1.29±0.20 vs. 0.14±0.06 mmHg/μl, p=0.004). At the same time point, the maximal slope of end-systolic pressure-volume relationship (Ees) decreased (0.5±0.2 mmHg/ml vs. 1.2±0.3, p<0.001). Consequently, right ventricular-arterial coupling was markedly deteriorated with a ≈50% decrease in the ratio of end-systolic to pulmonary artery elastance (Ees/Ea). Finally, left ventricular preload diminished (≈30% decrease in left ventricular end-diastolic volume). Histology demonstrated medial hypertrophy and small artery luminal narrowing. Chronic exposure to aorto-caval shunt is a reliable model to produce right ventricular volume overload and secondary pulmonary arterial hypertension. This model could be an alternative with low mortality and high reproducibility for investigators on the underlying mechanisms of shunt-related pulmonary hypertension.